I've been sucessful seasoning plated pieces using the following:
1.) Clean in lye as electrolysis will affect the plating
2.) Coat entirely (plated and worn areas) with solid Crisco
3.) Heat in oven at 230 F for 15-20 minutes
4.) Wipe off all excess melted Crisco with a paper towel
5.) Back in oven at 230 F for another 15-20 minutes
6.) Wipe thoroughly with paper towel
7.) Back in oven at 250-260 F for 30 minutes
8.) Wipe thoroughly with paper towel
9.) Back in oven for about one hour at 290-300 F
10) Let cool and you should have thin dry polymerized coating on the surface of the piece. For a thicker more durable seasoning, repeat Steps 2 thru 9 but I don't find it necessary. We just start cooking in it and let the natural seasoning process take over. Times above are not critical. Any oily "puddles" left on the iron as you heat it toward 300 F just forms a "gooey mess". Many other seasoning recipes work; this is one that I have found works well for me. It also allows you to rub your piece of cast iron a few more times to feel that fine surface .
Roy Meadows
